Throughout history, sleepwalkers have cooked meals, rode motorcycles, and committed murders—and it happens to far more of us than we think.

One night in 1987, a Canadian man named Kenneth Parks drove for 14 miles from his house to his in-laws. He then broke in and made his way upstairs, bludgeoning his mother-in-law with a crowbar that he’d gotten from the boot of his car before stabbing her repeatedly to death. He then proceeded to choke and stab his father-in-law, who miraculously survived. Parks then drove himself to the police station and turned himself in.

It sounds like a fairly cut and dry murder case, but after going to trial, Kenneth Parks walked free. Thanks to a combination of a lack of motive, his consistent version of events, and data gathered from EEG readings, no charges were pressed against him because all evidence pointed to the unlikely and bewildering truth that Parks had been sleepwalking. It remains one of the most remarkable cases of homicidal sleepwalking in history.

Sleepwalking—traditionally referred to as somnambulism—takes place during NREM, which is the deepest form of dreamless sleep. In 2012, a groundbreaking study published in the American medical journal of Neurology found that around 30 percent of participants had a history of sleepwalking at some point in their lifetime (a figure far higher than previously thought), which suggests nearly a third of us have or could experience the phenomenon. Although it’s thought to be triggered by stress, anxiety, and alcohol, it is totally unknown why we do it. Are we simply on auto-pilot? Trying to fulfill our fantasies? Or perhaps something stranger…

Science hasn’t always provided satisfactory answers to the many questions raised around sleepwalking. Throughout history, the mysteries of somnambulance have lead many to come up with their own theories—drawing on spirituality, pseudo-science, and folklore—with sleepwalkers seeming to exist somewhere between this world and another.

The sleepwalking scene in Shakespeare’s Macbeth (Act V, Scene I) is as iconic as it is unsettling. As Lady Macbeth sleepwalks, she emotionally recalls the murders of Lady Macduff, Banquo, and Duncan, incriminating herself in the process. Seemingly possessed by an unknown energy, she refers to the metaphorical blood on her hands: “Will these hands ne’er be clean?... Here’s the smell of blood still… All the perfumes of Arabia will not sweeten this little hand! Oh, oh oh!”

In the book Wild Nights: How Taming Sleep Created Our Restless World, Benjamin Reiss tells the story of Rachel Baker, a Presbyterian Christian from early 19th Century New York, who would preach, pray, and curse in her sleep. Baker, who was known as “The Sleeping Preacher,” started to gather onlookers and disciples that would sit around her bed to hear her "evening exercises," sometimes drawing crowds of up to 300 people.

During these trance-sermons Baker gave deranged warnings of “the shuddering terrors of eternal damnation” while grinding her teeth, groaning, and breathing irregularly. She would gaze at the visitors with an “unsteady, wild, and capricious eye” and an “unusual, sickly dilation of the pupil.” To add to the drama, when her nocturnal episodes had finished, she would shake violently and collapse.

Marion Cotillard as Lady Macbeth (a still taken from the 2015 Hollywood remake of Macbeth)

Sleepwalkers have been viewed through a veil of mysticism. German philosopher and scientist, Dr. Carl Reichenbach, did extensive research into sleepwalking in the 18th Century. After studying hundreds of sleepwalkers, he linked the phenomena to his theory of "Odic Force," of which he dedicated his final years alive to studying.

"Odic Force," named after the Norse god Odin, is a theoretical field of “vital energy” that, according to Dr. Reichenbach, combined electricity, magnetism, and heat and emanates from many things on our planet, including humans, plants, and magnets. The scientist also linked the disorder to lunar phases, stating that the sleepwalking “lunatics” he studied were affected more during a full moon. In his research, some of his subjects were observed sleepwalking precariously atop high precipices reaching out toward the moon. Although well received in occultist circles, his theories were highly criticized by the mainstream science world and have since been banished to the drawer labeled "pseudoscience."

Fast-forward to 1915 and Sigmund Freud, the founding father of psychoanalysis, also developed a fascination with somnambulists. Perhaps unsurprisingly, he linked sleepwalking with the fulfilling of repressed sexual desires. He also theorized that sleepwalkers were attempting to return to the area where they used to sleep as a child.

Five years later, sleepwalking made one of its first major appearances on the silver screen via the film The Cabinet of Dr. Caligari. This prophetic silent horror from Germany told the story of a wicked doctor who uses a sleepwalker to commit murders. A stylish and spiraling movie, it manages to tap into the appeal of the mysteries of sleepwalking, while questioning what we understand as sanity and consciousness.

Despite the many mysteries of sleepwalkers, there are scientists out there right now trying to crack the complexities of a semi-waking mindset. Dr. Guy Leschziner is a neurologist at Guy's & St. Thomas' Hospitals in London and he runs one of the largest sleep clinics in the UK. They offer therapy and treatment to sleepwalkers, insomniacs, and others suffering from sleep disorders. His patients include people who have ridden motorcycles, driven cars, and committed crimes while being asleep.

Dr. Leschziner writes, “We used to consider sleep and wake to be binary states—that people are either awake or asleep. These remarkable conditions [sleepwalking] tell us that this is not the case. In fact, being asleep and awake are at the opposite ends of a continuum, a spectrum of brain activity. Depending where on that spectrum our brain is defines our behavior, our recollection, and our abilities.”

The takeaway here is that we are never fully awake or fully asleep, but rather a percentage of both at all times. This explains how Jackie, one of Dr. Leschziner’s patients, awakes and rides her motorcycle in the middle of the night while she’s sleepwalking. The cognitive parts of her brain that control her driving skills, gear-changing and balance are awake, while much of the rest of her brain is asleep. However, where she goes at night, and why, is a mystery.

The estimate that 30 percent of us will sleepwalk at some point in our life might seem a little high, but the real figure may be much higher. A definitive statistic is hard to find because it is so difficult to gauge. For those of us that live alone, we might make somnambulant journeys without ever knowing—cooking food or completing tasks before returning to bed inconspicuously. Jackie only found out that about her midnight journeys when her neighbors brought it to her attention.

Just as Banquo warns Macbeth that “the instruments of darkness tell us truths,” so too might our nocturnal adventures tell us some hidden truths about ourselves. What those truths are, however, are yet to be fully understood.